Exhaust stream mixer

ABSTRACT

An exhaust nozzle for a turbine engine includes multiple daisy style corrugations arranged circumferentially about the exhaust nozzle. Each of the daisy style corrugations has a radially inner base portion and multiple lobes protruding radially outward from the base portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/832,198, which was filed on Jun. 7, 2013, and to U.S. patentapplication Ser. No. 14/298,331 each of which are incorporated herein byreference.

TECHNICAL FIELD

The present disclosure is related toward a corrugated exhaust nozzle fora gas turbine engine, and more specifically toward an exhaust nozzleincorporating multiple daisy style corrugations.

BACKGROUND OF THE INVENTION

Gas turbine engines, such as those used to drive propellers in acontra-rotating prop-fan engine, utilize compressed and expanded gassesto produce rotational motion. Such engines include a compressor section,a combustor section, and a turbine section which work cooperatively todrive a shaft. A gas flowpath passes through each of the compressor,combustor and turbine sections and fluidly connects them. Also connectedto the shaft, aft of the turbine section, are multiple propellers whichgenerate thrust.

Heated exhaust gasses from the turbine section of the gas turbine enginecontact the roots of the propeller blades after being expelled from theturbine section. If the exhaust gasses do not have sufficient time tocool by mixing with ambient air prior to the gasses contacting thepropeller blades, the excess heat of the gasses can wear the propellerblades significantly reducing the propeller blade life and possiblydamaging the propeller blades.

In order to mitigate this effect, the prior art has relied on applyingcostly thermal barrier coatings to the affected areas of the blades toprevent damage from the hot exhaust gasses. Such methods are undesirablein some engines as they require periodic checks and periodic maintenanceof any damaged thermal barrier coatings. Thermal barrier coating systemsalso include a potential risk of in-flight thermal barrier coatingdamage which can lead to damage to the propeller blades and affect theavailable thrust.

SUMMARY OF THE INVENTION

A turbine engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a compressor section, acombustor in fluid communication with the compressor section, a turbinesection in fluid communication with the combustor, an exhaust nozzle influid communication with the turbine section, the exhaust nozzleincludes a plurality of exhaust stream mixers circumferentially disposedabout the exhaust nozzle, each of the exhaust stream mixers includes aradially inward base portion and a plurality lobes protruding radiallyoutward from the base portion.

In a further embodiment of the foregoing turbine engine, each of theexhaust stream mixers is defined by a single continuously curved wall.

In a further embodiment of the foregoing turbine engine, each of theexhaust stream mixers is further defined by a cross section normal to anaxis defined by the turbine engine, the cross section has acircumferential length at least twice the circumferential length of acircle inscribing the exhaust stream mixer.

In a further embodiment of the foregoing turbine engine, each of thebase portions is defined by a pair of convex walls.

In a further embodiment, the foregoing turbine engine further includesat least four exhaust stream mixers.

In a further embodiment, the foregoing turbine engine further includesat least 8 exhaust stream mixers.

In a further embodiment of the foregoing turbine engine, each of theexhaust stream mixers has a radial height less than one half the totalradius of the exhaust nozzle.

In a further embodiment of the foregoing turbine engine, each of theexhaust stream mixers has a radial height of less than one quarter thetotal radius of the exhaust nozzle.

In a further embodiment of the foregoing turbine engine, each of theexhaust stream mixers is defined by at least three radially protrudinglobes and a valley between each of the radially protruding lobes andeach adjacent of the radially protruding lobes.

In a further embodiment of the foregoing turbine engine, each of thelobes has a smaller cross sectional area than the base portion.

A method for mixing exhaust gas exiting an exhaust nozzle of a turbineengine according to an exemplary embodiment of this disclosure, amongother possible things includes passing exhaust gasses through an exhauststream mixer, the exhaust stream mixer includes at least one daisy stylecorrugation, thereby generating stream-wise vortices and transversevortices in the exhaust stream.

In a further embodiment of the foregoing method, the step of passing theexhaust gasses through an exhaust stream mixer includes passing the gasthrough an exhaust stream mixer defined by at least a base portionhaving two convex walls and a plurality of lobes extending radiallyoutward from the base portion, thereby maximizing a circumference of theexhaust nozzle while maintaining a desired cross sectional area.

In a further embodiment of the foregoing method, the step of passing theexhaust gasses through the exhaust stream mixer further includesmaturing the vortices until the vortices are of sufficient size thateach of the vortices interfaces with adjacent vortices.

In a further embodiment of the foregoing method, the stream-wisevortices and the transverse vortices facilitate intermixing between theexhaust gasses and a surrounding ambient air flow.

In a further embodiment of the foregoing method, the intermixing betweenthe exhaust gasses and the surrounding ambient air flow cools theexhaust gasses prior to the exhaust gasses contacting a propeller blade,thereby protecting the propeller blade from thermal stresses.

An exhaust nozzle according to an exemplary embodiment of thisdisclosure, among other possible things includes an axis defined by theexhaust nozzle, a cross section of the exhaust nozzle normal to the axisincludes a plurality of daisy style corrugations, each of the daisystyle corrugations further comprises a radially inner base portion, anda plurality of lobes protruding radially outward from said base portion.

In a further embodiment of the foregoing exhaust nozzle, each of thedaisy style corrugations is defined by a plurality of convex sidewalls.

In a further embodiment of the foregoing exhaust nozzle, each of theplurality of lobes has a smaller cross sectional area than the basesection.

In a further embodiment of the foregoing exhaust nozzle, the daisy stylecorrugation is constructed of a single continuous wall.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a contra-rotating prop-fan engine.

FIG. 2 schematically illustrates an exhaust nozzle section of thecontra-rotating prop-fan engine of FIG. 1.

FIG. 3 illustrates a cross sectional aft view of the exhaust nozzle ofthe contra-rotating prop-fan engine of FIG. 1.

FIG. 4a illustrates a cross section of an example daisy stylecorrugation for use in an exhaust nozzle.

FIG. 4b illustrates an isometric view of the exhaust nozzle of FIG. 3 a.

FIG. 5 illustrates a cross section of an alternate example daisy stylecorrugation for use in an exhaust nozzle.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 illustrates a contra-rotating prop-fan engine 10 used to generatethrust for an aircraft. The engine 10 includes a compressor section 20,a combustor section 30, and a turbine section 40. The compressor section20, combustor section 30, and the turbine section 40 work cooperativelyto rotationally drive a shaft 70 along the engine's central axis A. Agas path fluidly connects each of the compressor section 20, combustorsection 30, and the turbine section 40. Gas, such as ambient air, isadmitted into the gas path at a gas inlet 50 on a fore end of thecontra-rotating prop-fan engine 10. Heated exhaust gas is expelled fromthe turbine engine section 40 out a nozzle 52 located in an exhaustnozzle section 54 of the engine 10. Connected to the concentric,contra-rotating shafts 72 and 70, and aft of the exhaust nozzle section54, are a pair of contra-rotating propellers 60, 62, respectively, thatgenerate thrust for the aircraft. The contra-rotating propeller 60 ismounted on a separate shaft 72. The separate shaft 72 is concentric tothe input shaft 70 and rotates in a direction opposite to the rotationof shaft 70 through a compact differential gearbox 74.

The heated exhaust gases from the turbine section 40 are expelleddirectly in front of (fore of) a radially inner portion of the leadingedge of the blades of the contra-rotating propellers 60, 62. These hotexhaust gases can reach temperatures as high as 950 F (510 C) duringoperation of the engine 10. Due to the high energy momentum of theexhaust gases, the exhaust gasses do not mix well with the ambient airflow surrounding the engine 10. If the exhaust gasses are not cooledbelow a certain threshold, the exhaust gasses affect the structuralintegrity of the blades of the propellers 60, 62. Further exacerbatingthis effect is the fact that in order to save weight and cost, theblades of the contra-rotating propellers 60, 62 are often manufacturedfrom epoxy resins, fiberglass, or other lightweight composite materialsand are unable to withstand high thermal stresses.

The mixing of the exhaust gases from the turbine section 40 with theambient air flow causes jet exhaust noise. The exhaust noise is furtherincreased by a shearing action caused by the disparity between therelative speeds between the exhaust gasses and the ambient air flow. Jetexhaust noise levels are undesirable and can be reduced by increasingthe mixing rate between the exhaust gasses and the ambient air flow, orwhen the exhaust gas velocity relative to the velocity of surroundingcold air flow is reduced. This effect is achieved by changing thepattern of the exhaust jet emanating from the exhaust nozzle 52. One wayof changing the pattern of the exhaust gas jet is by including exhauststream mixers, such as corrugations, at the exhaust nozzle 52. Inaddition to noise mitigation, corrugated exhaust nozzles 52 allow moreefficient hot gas/cold ambient air mixing which improves the overallefficiency of the engine 10 and lowers the temperature of the exhaustgas stream.

FIG. 2 illustrates a zoomed-in exhaust nozzle section 54 of thecontra-rotating prop-fan engine 10 of FIG. 1 including the abovedescribed corrugations. A gas path 120 proceeds from the turbine section40, illustrated in FIG. 1, and funnels the exhaust gasses to an exhaustnozzle 52 that expels the gasses out of the engine 10. Ambient air 110surrounds the engine 10, and is at a lower temperature relative to theexhaust gasses. Due to the speeds and temperatures of the exhaustgasses, relative to the ambient air 110, a boundary layer 112 separatesthe ambient air 110 from the exhaust gasses.

The exhaust nozzle 52 is shaped with multiple deep daisy stylecorrugations that function as efficient exhaust stream mixers. Each ofthe daisy style corrugations is defined by multiple lobes defining peaks148, valleys 146, and a base portion 142. The particular shaping of thedaisy style corrugations imparts both an axial swirl and acircumferential swirl on the exhaust gasses emanating from the gas path120. The specifics of the swirling are discussed in greater detailbelow. The swirling aids in breaking down the boundary layer 112,resulting in a swirling mixture 130 of the exhaust gasses and theambient air 110. The swirling mixture 130, in turn, cools the exhaustgasses prior to the exhaust gasses contacting the propeller blades 60,62, thereby minimizing wear on the blades.

Daisy style corrugations provide a large ratio of circumference area tocross sectional area of the nozzle 52. In some instances, the daisystyle corrugations are limited by performance penalties that restrictthe depth of each corrugation, the number of corrugations, or the numberof lobes in each corrugation. In order to prevent backpressure and otherpenalties, the daisy style corrugated nozzle 52 maintains the same crosssectional area as known basic ring shaped nozzles of the prior art.

FIG. 3 schematically illustrates an aft cross sectional view of thenozzle 52 of FIG. 2 and provides a cross sectional view of the daisystyle corrugations 210 of the exhaust nozzle 52. The engine 200 includesa shaft 220 and a turbine section 230 defined about the shaft. Arrangedcircumferentially about the turbine section 230 are the multiple daisystyle corrugations 210 through which exhaust gasses are emitted from theturbine section 230. In the particular illustrated example, eight daisystyle corrugations 210 are utilized. It is understood that theparticular number of daisy style corrugations 210 utilized can bealtered depending on the specifications of the particular engine 200.Each of the daisy style corrugations 210 defines an exhaust gas opening250 that expels exhaust gas from the exhaust nozzle 52 into the ambientair flow 240 surrounding the engine 200.

Daisy style corrugations 210 are defined by a relatively wide baseportion 212 having convex walls and multiple lobes 216 (alternatelyreferred to as petals) extending radially outward from the base section212. A base section width 262 is defined as the shortest distance acrossthe base section 212. A radial height 260 of each daisy stylecorrugation 210 is defined as the distance that the daisy style extendsradially outward from the turbine section 230. Defined between each lobe216 and each adjacent lobe 216 in a single daisy style corrugation 210is a valley 214. In contrast, prior art corrugations are defined by asingle peak/valley per corrugation or a wave shaped pattern. Asdescribed above, the introduction of the lobed daisy style corrugations210 as exhaust stream mixers increases the mixing between the exhaustgasses and the ambient air 240 in a turbulent jet in a number of ways.

First, the convolution of the lobes 216 increases the initial interfacearea between primary and secondary flows relative to prior artcorrugations and ring nozzles. The combination of lobes 216 and valleys214 imparts an axial swirl (aligned with the shaft 220) on the exhaustgasses. The axial swirls are alternately referred to as streamwisevortices, and a circumferential swirl (tangential to the circumferenceof the engine 200) on the exhaust gasses, the circumferential swirls arealternately referred to as transverse vortices, on the exhaust gassesexiting the nozzle. The tangential swirls aid in breaking down theboundary layer 112 (illustrated in FIG. 2). The tangential swirls alsoincrease the rate at which the exhaust gasses mix with the ambient air240.

A second way that the daisy style corrugations increase mixing drivesfrom the stream-wise vortices. The stream-wise vortices increase theinterface area between the exhaust gasses and the ambient air 240 due toan interaction between counter rotating vortices. A cross streamconvection associated with the stream-wise vortices increases theinterface gradients between the ambient air and the exhaust gassesthereby further increasing the mixing.

Furthermore, by imparting the streamwise and transverse vortices on theexhaust gas, the instability of the boundary layer 112 between theexhaust gas and the ambient air is increased (causing the boundary layer112 to break down faster) and the mixing rate is increased. Horseshoevortices can also be generated in the exhaust stream as a result of thedaisy style corrugations 210; however, their impact on the overallmixing between the exhaust gasses from the nozzle 52 and the ambient air240 is minimal compared to the effects from the streamwise andtransverse vortices.

FIG. 4a illustrates an example daisy style corrugation exhaust streammixer 300 for use in a nozzle 52. FIG. 4b illustrates an isometric viewof the daisy style corrugation exhaust stream mixer 300. In addition tothe enhancement to the mixing processes provided by the daisy stylecorrugations (described above), the introduction of the stream-wisevortices resulting from the daisy style corrugations substantiallyalters the flow field as compared to prior art corrugations (defined byalternating peaks, and valleys arranged circumferentially around thenozzle). In daisy style corrugation, each lobe 310 produces a pair ofcounter rotating vortices 350, 360 in the exhaust stream. The vortices350, 360 increase in size as they travel away from the nozzle 52. Thisincrease in size is referred to as maturing. As the vortices mature,they effectively twist the hot exhaust gas flow from the nozzle 52 andthe cold bypass flow from the ambient air together in a helical manner.As the vortices move downstream from the nozzle, they grow due toturbulent diffusion and thermal dissipation and begin to interact withthe vortices produced by the adjacent lobe, thereby further increasingthe mixing rate.

The daisy style corrugation exhaust stream mixer 300 also provides alarger circumference of the exhaust nozzle relative to a ring nozzle orstandard corrugation without increasing the cross sectional area. Thecircumference of the exhaust nozzle in a ring nozzle is C_(n)=πD_(n),where C_(n) is the circumference of the exhaust nozzle and D_(n) is thediameter of the exhaust nozzle. Inclusion of daisy style corrugationssuch as is illustrated in FIGS. 3 and 4 provide 8-9 times thecircumferential length for the same overall nozzle diameter. By way ofexplanation, the overall nozzled diameter of the daisy style corrugatednozzle is the diameter of a circle that would circumscribe the daisycorrugated nozzle, and the overall nozzle diameter of a non-corrugatednozzle is the diameter of the nozzle. Similarly, the overall diameter ofa nozzle including standard wave corrugations is the diameter of acircle circumscribing the wave corrugations.

A typical daisy style corrugation's circumference is approximately twicethe circumference of the circle in which the corrugation can beinscribed. Hence, to increase the overall circumference of a nozzle 52by a factor of eight, four daisy style corrugations are used. The daisystyle corrugations provide the added benefit of reducing the overalldiameter of the nozzle 52. In one example, we use eight daisy stylecorrugations, for an exhaust nozzle 52 with a diameter of 300 mm; therequired average height of each lobed mixer is ¼ of the overall diameterof nozzle 52, 75 mm. Further increasing the number of the daisy stylecorrugations leads to even smaller requirements for individual mixerheights. The optimal design is dictated by the specific engineparameters, including cost, for a specific installation.

The increased surface area of the daisy-style exhaust nozzle, relativeto existing ring nozzles or known corrugated nozzles having the samecross sectional area allows for significant improvements in cooling. Inone example the heated exhaust gasses can be cooled to around 450 F (230C) using the daisy style corrugations. This low temperature allows thepropeller blades to be created of lower heat tolerant materials, such asphenolic-composite resin, without the need for turbine blade coatings oractive cooling.

Referring now to FIG. 5, an alternate daisy style corrugated exhaustmixer 500 is illustrated. As can be seen, each of the daisy stylecorrugations 510 is defined by a wide based portion 512 having convexsidewalls 514. Protruding radially outward from the wide base portion512 are multiple lobes 516 (peaks) defining a valley 518 between eachlobe 516 and each adjacent lobe 516.

As can be seen the number of lobes 516 can be increased beyond three,with a corresponding increase in the circumference of the daisy stylecorrugation 500. To compensate for the decrease in lobe 516cross-sectional area resulting from an increase in the number of lobes516, the base section is enlarged, thereby maintaining a consistentexhaust nozzle cross sectional area and preventing excessive backpressure at an exhaust nozzle.

Further defining daisy style corrugations 500 is the continuous natureof the walls 520, 522 defining the base portion 512 and the lobes 516.The walls 520, 522 are continuous in order to prevent corners or grooveswhich act as stress risers, and where debris (i.e., dust, sand, soot,dirt, grime, etc.) can build up.

As can be appreciated by one of skill in the art having the benefit ofthis disclosure, the particular lengths, widths and numbers of theproposed daisy-style lobes can be selected to tailor the above describedaffects to a particular engine or configuration while still fallingwithin the above disclosure.

It is further understood that any of the above described concepts can beused alone or in combination with any or all of the other abovedescribed concepts. Although an embodiment of this invention has beendisclosed, a worker of ordinary skill in this art would recognize thatcertain modifications would come within the scope of this invention. Forthat reason, the following claims should be studied to determine thetrue scope and content of this invention.

The invention claimed is:
 1. A method for mixing exhaust gas exiting anexhaust nozzle of a turbine engine comprising the step of: passingexhaust gasses through at least one exhaust stream mixer of a pluralityof exhaust stream mixers thereby generating stream-wise vortices andtransverse vortices in said exhaust stream, wherein said at least oneexhaust stream mixer comprises a daisy style corrugation, the at leastone exhaust stream mixer is defined by a cross section normal to an axisdefined by the turbine engine, wherein the cross section has a lengthextending the entire circumference of the cross section at least twicean entire length of a circumference of a circle circumscribing the crosssection normal to the axis of the turbine engine.
 2. The method of claim1, wherein said step of passing said exhaust gasses through the at leastone exhaust stream mixer, comprises passing said gas through the atleast one exhaust stream mixer defined by at least a base portion havingtwo convex walls and a plurality of lobes extending radially outwardfrom said base portion.
 3. The method of claim 1, wherein the step ofpassing said exhaust gasses through said at least one exhaust streammixer further comprises maturing vortices until said vortices are ofsufficient size that each of said vortices interfaces with adjacentvortices.
 4. The method of claim 1, wherein said stream-wise vorticesand said transverse vortices facilitate intermixing between said exhaustgasses and a surrounding ambient air flow.
 5. The method of claim 4,wherein said intermixing between said exhaust gasses and saidsurrounding ambient air flow cools said exhaust gasses prior to saidexhaust gasses contacting a propeller blade, thereby protecting saidpropeller blade from thermal stresses.
 6. A turbine engine comprising: acompressor section; a combustor in fluid communication with thecompressor section; a turbine section in fluid communication with thecombustor, an exhaust nozzle in fluid communication with the turbinesection; said exhaust nozzle comprising a plurality of exhaust streammixers circumferentially disposed about said exhaust nozzle, whereineach of said exhaust stream mixers includes a radially inward baseportion and a plurality lobes protruding radially outward from said baseportion, and the exhaust stream mixer is defined by a cross sectionnormal to an axis defined by the turbine engine, wherein the crosssection has a length extending the entire circumference of the crosssection at least twice an entire length of a circumference of a circlecircumscribing the cross section normal to the axis of the correspondingstream mixer of each of said plurality of exhaust stream mixers.
 7. Theturbine engine of claim 6, wherein each of said exhaust stream mixers isdefined by a single continuously curved wall.
 8. The turbine engine ofclaim 6, wherein each of said base portions is defined by a pair ofconvex walls.
 9. The turbine engine of claim 6, wherein furthercomprising at least four exhaust stream mixers.
 10. The turbine engineof claim 9, further comprising at least 8 exhaust stream mixers.
 11. Theturbine engine of claim 6, wherein each of said exhaust stream mixershas a radial height less than one half the total radius of the exhaustnozzle.
 12. The turbine engine of claim 11, wherein each of said exhauststream mixers has a radial height of less than one quarter the totalradius of the exhaust nozzle.
 13. The turbine engine of claim 6, whereineach of said exhaust stream mixers is defined by at least three radiallyprotruding lobes and a valley between each of said radially protrudinglobes and each adjacent of said radially protruding lobes.
 14. Theturbine engine of claim 6, wherein each of said lobes has a smallercross sectional area than said base portion.
 15. An exhaust nozzlecomprising: an axis defined by the exhaust nozzle, wherein a crosssection of the exhaust nozzle normal to said axis includes a pluralityof daisy style corrugations; each of said daisy style corrugationsfurther comprises a radially inner base portion, and a plurality oflobes protruding radially outward from said base portion; and each ofsaid daisy style corrugations is defined by a cross section normal to anaxis defined by a turbine engine, wherein the cross section has a lengthextending the entire circumference of the cross section at least twicean entire length along a circumference of a circle circumscribing thecross section normal to the axis of the corresponding stream mixer ofeach of said plurality of exhaust stream mixers.
 16. The exhaust nozzleof claim 15, wherein each of said daisy style corrugations is defined bya plurality of convex sidewalls.
 17. The exhaust nozzle of claim 16,wherein each of said plurality of lobes has a smaller cross sectionalarea than said base section.
 18. The exhaust nozzle of claim 16, whereinsaid daisy style corrugation is constructed of a single continuous wall.